Polyamides are a group of macromolecules with repeating units linked by amide bonds (such as O═C—NH—C). Artificial polyamides relate to materials such as nylons, aramids, and sodium poly(aspartate). Polyamides may relate to aliphatic polyamides, such as PA6 and PA 66, polyphtalamides, such as PA 6T, and aramides. Synthetic polyamides are commonly used in textiles, automotive applications, carpets and sportswear due to their high durability and strength. The transportation industry is the major consumer, accounting for 35% of polyamide (hereinafter also referred to as PA) consumption;
In various applications, such as in carpets, the polyamides are mixed with further materials and additives. One of the main materials being present is a polyester material-called polyethylene terephthalate (PET). In addition further additives may be present, typically fillers and the like.
For re-using the raw materials the various components need to be separated effectively. The amount of materials that are currently re-used in the Netherlands only is already 400 ktons per year, which is already a huge amount. A proper separation process is therefore needed.
Some prior art processes are known. U.S. Pat. No. 5,430,068 A recites a process for recovering aliphatic polyamide from admixtures thereof with foreign materials comprising the steps of: (1) dissolving the polyamide at an elevated temperature in a solvent selected from the group consisting of a substantially anhydrous ethylene glycol, propylene glycol, and aliphatic carboxylic acid having from 2 to 6 carbon atoms; (2) separating any insoluble foreign material from the polyamide solution; (3) combining the polyamide solution with an additional quantity of substantially the same solvent at a temperature sufficiently below the temperature of the solution to quench the solution and cause the polyamide to precipitate; and (4) recovering the polyamide precipitate. This procedure is considered somewhat cumbersome in view of process steps. In addition water, typically being present especially in a washed waste material, is excluded from the process. In addition it is preferred to use acidic conditions. For neutralizing an amount of base is then required, and as a result typically a salt is obtained. As such the process is relatively costly.
WO00/29463 discloses a further process for the separation of different polyamides, especially PA6 and PA6,6 (also known as nylon 6 and Nylon 6,6). Use is made of ethylene glycol or particularly glycerol as a solvent. The nylons will dissolve in highly pure glycerol upon heating to 205° C. Upon cooling, first the PA6,6 and subsequently the PA6 will precipitate. When the PA6,6 has been precipitated, but the PA6 is still in solution, the mixture can be filtrated, resulting in a separation. Finally, the PA6 may be recovered by precipitation and washing with water, for instance at 40° C. According to said patent application, the process of heating and selective precipitation is preferably repeated several times to increase purity.
Again, the solvent is highly pure glycerol and water is excluded. One of the reasons is that a mixture of water and glycerol is slightly basic and may further corrode metal of the vessel to get slightly acid. Both in slightly acid and in slightly basic conditions at a high temperature, hydrolysis may occur. This is undesired for the polyamide, as it makes it more difficult to recover the water soluble amide oligomer.
Alternative processes for separation of polyamides therefore use a mixture of water and lower alkyl alcohols with a single alcohol group, such as methanol, ethanol, isobutanol, as described in U.S. Pat. No. 2,742,440 and WO02/36668, for instance. However, the precipitation of nylon would start around 160° C., with the risk that the nylon precipitates onto the polyester fibres, such as PET fibres. This would significantly hinder separation of the polyester from the polyamide. Moreover, in order to keep the water sufficiently liquid above its boiling point, higher pressures are needed. This however is disadvantageous in that the waste material often has a very low density. Such very low density material is preferably added in portions into the reactor, and a volume reduction may occur. To combine this with significantly higher pressures is deemed less practical.
Therefore there still is a need for an improved separation process which is more cost effective, simple, and is more robust/without generating further waste streams such as salts.
The present invention provides an improved method of removing additives and an additive capturer e.g. for degrading polymers which overcomes at least one of the above disadvantages, without jeopardizing functionality and advantages.